This is a simple and easy to make serial keypad. The microcontroller 16F88 will output the number of the push button pressed.

This project can be used for many different purposes. Probably the most used application would be to interface to any electronic project that requires a keypad. There are several ready made keypads on the market, but those work with matrix connections and require 7 pins for a 12 button pad. For new programmers, matrix keypads can be a bit tricky to program.

My circuit can use from 4 up to 12 push buttons with only one wire connection ( plus ground pin ) and the data in RS232, making possible to use a small microcontroller like an 8 pin to use this keypad. It’s also built in a setup mode where it’s possible to change the key output rate. This setting is saved in the microcontroller’s memory.